Activated alumina Claus catalyst having increased sodium oxide content

ABSTRACT

An improved Claus catalyst comprising activated alumina in which sodium oxide concentration is controlled to achieve increased sulfur conversion. Sodium oxide is present in an amount greater than 0.50 wt % (1100° C. calcined basis), the remainder being activated alumina. Specific surface area is greater than 100 m 2  /g (BET). In a preferred embodiment, sodium oxide content is controlled in the range 1.0 to 2.5 wt %. The catalyst preferably has a surface area greater than 300 m 2  /g (BET) and an LOI (hydroxyl content as determined by heating from 400° to 1100° C.) between 2.0 and 6.0 wt %.

This application is a continuation of U.S. Ser. No. 170,638, filed July21, 1980, now U.S. Pat. No. 4,364,858.

BACKGROUND OF THE INVENTION

The present invention relates to an improved Claus catalyst. Moreparticularly, it provides an improved Claus catalyst made from activatedalumina and sodium oxide; the catalyst possesses increased resistance tosulfate poisoning and higher catalytic activity with respect tocompounds such as H₂ S, SO₂, COS and CS₂ than the catalysts of the priorart.

Many industrial fuels contain sulfur compounds which are toxic,corrosive and produce sulfur dioxide when burned. It is necessary,therefore, to remove these sulfurous materials for economic andecological reasons prior to utilization of the fuel. In the case ofcrude oil, for example, the oil is typically subjected tohydrodesulfurization (i.e. treatment with hydrogen and acobalt-molybdenum on alumina catalyst) to produce hydrogen sulfide inconjunction with ammonia, water and diluents. In the case of sournatural gas, hydrogen sulfide and carbon dioxide are usually present inconcentrations which can be removed by conventional sweetening processessuch as those described in C. D. Swaim, Jr.'s article entitled "GasSweetening Processes of the 1960's", found in Hydrocarbon Processing,49(3), 127 (1970). Sweetened sour natural gas by-products and theoff-gas from hydrodesulfurization of crude oil are each rich in hydrogensulfide and may be used, therefore, as feed gases for the well-knownClaus process. Basically, in the Claus process, one-third of the totalhydrogen sulfide present in the gas to be treated is burned in a furnacewith air to produce sulfur dioxide at temperatures between 900° and1200° C. The remaining two-thirds of the hydrogen sulfide react on thecatalyst at temperatures of 200° to 400° C. with the sulfur dioxide soproduced to form sulfur and water vapors. A low temperature Clausprocess is used to condense sulfur on the catalyst at temperatures ofabout 25° to 200° C. However, at high furnace temperatures, sidereactions also occur in which COS and CS₂ are formed. Thesecarbon-sulfur compounds may be removed by catalytic reaction with sulfurdioxide to form carbon dioxide and sulfur and to a lesser degree bycatalytic reaction with water vapor to form carbon dioxide and hydrogensulfide.

Although the amount of COS and CS₂ formed by high temperature sidereactions may only amount to a few percent of the sulfurous materialpresent in the emitting furnace gas, increasingly more stringent airregulations make their removal from the gas necessary. Conversion ofthese carbon-sulfur compounds to sulfur is difficult, however, becauseof their slow reaction rates. Further, the optimum reaction conditionsfor each of the carbon-sulfur compounds differ significantly. Removal ofthese organic sulfur compounds is also complicated by the presence ofsulfurous gas which inhibits hydrolysis of the carbon derivatives ofsulfur, and, as already indicated, it is believed that hydrolysis ispartially responsible for conversion of these carbon-sulfur compounds.Therefore, only the most active of catalysts would be capable ofremoving these organic sulfur compounds after sulfate formation fromsulfur dioxide. Considerable efforts to find such an extraordinarilyactive catalyst have been exerted in the past few years. Renault et al(U.S. Pat. No. 3,845,197) describes a process of first reacting the gasstream containing carbon-sulfur compounds such as COS and CS₂ with steamwhile passing the gas stream over an alumina-containing catalyst at 250°to 400° C. to produce H₂ S. A portion of the H₂ S produced is thenoxidized at 300° to 500° C. to produce SO₂ in an amount sufficient toestablish a ratio of H₂ S to SO₂ of 1.6 to 3. The SO₂ is then reactedwith the remaining portion of H₂ S at 20° to 160° C. to produceelemental sulfur. The catalyst used by Renault et al to produce the H₂ Sis alumina in which one or more metals such as molybdenum, tungsten,iron, nickel or cobalt, may be present as oxides. The catalyst has analkali metal content lower than 0.1%, a specific surface area of 40 to500 m² /g and a pore volume of 10 to 80 cc/100 g. Oxidation of the H₂ Sto SO₂ is then carried out in the presence of a second catalyst (i.e.oxidation catalyst) which may be alumina in which chromium, vanadium,iron or mixtures thereof are present. The oxidized gas stream is thencontacted at 20° to 160° C. with an organic solvent which contains acatalyst favoring the reaction between H₂ S and SO₂. The catalystdescribed as useful in this stage of the treatment is an alkali metalcompound. The Renault et al approach divides the gas treatment intothree separate stages with a different catalyst for each of thesestages. Such a detailed procedure is both expensive and difficult to usein a commercial operation.

Pearson et al (U.S. Pat. No. 3,725,531) discloses a less complicatedprocess for treating off-gases containing organic sulfur compounds inwhich the off-gas is contacted with an alumina base catalyst to convertthe organic sulfur materials to carbon dioxide and elemental sulfur. Thecatalysts described as useful in the practice of the Pearson et alprocess include an alumina base support in combination with at least onemetal selected from strontium, calcium, magnesium, zinc, cadmium, bariumand molybdenum. These catalysts, it is claimed, have a high resistanceto sulfate poisoning, i.e. the buildup of sulfate on the surface of thecatalyst due to oxidation of sulfur dioxide on the active sites of thecatalyst employed. Pearson et al state that suitable alumina basesupports for the catalyst include activated bauxite, activated aluminaspossessing an essentially chi-rho structure, calcined Bayer hydrate,calcined gel-derived aluminas containing a substantial portion ofpseudoboehmite and gamma alumina. It is the promoter (i.e. Ca, Mg, Cd,etc.), however, which acts as an antipoisoning agent to provideincreased alumina resistance to sulfate poisoning. However, the amountof antipoisoning agent included in the catalyst, and consequently theeffectiveness of the Pearson et al catalyst, is substantially dependentupon economy of manufacture.

Daumas et al also disclose improved Claus catalysts in U.S. Pat. Nos.3,978,004, 4,054,642 and 4,141,962 in which an activated aluminacomprises the largest component. In U.S. Pat. No. 3,978,004, theactivated alumina is combined with a compound of lanthanum, a lanthanideseries metal of atomic number 58 to 71 or a metal of Group IIIB. In U.S.Pat. No. 4,054,642, the alumina is combined with a metal of Group IIIAof the periodic chart. And in U.S. Pat. No. 4,141,962, the alumina iscombined with a titanium compound. These promoters (like the Pearson etal promoters) are rather esoteric solutions to the problem of sulfatepoisoning of the catalyst. Though a variety of promoters have beentried, there still exists a need for an alumina Claus catalyst which ishighly resistant to sulfate poisoning.

In view of the above-discussed problems, it would be particularlyadvantageous to have available a Claus catalyst which is highlyresistant to sulfate poisoning, is relatively cheap to make (i.e.requires no expensive promoter), increases catalytic activity andrequires no complication of the standard Claus conversion procedure.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved Clauscatalyst which is highly resistant to sulfate poisoning.

It is also an object of the present invention to provide an improvedClaus catalyst which may be used in existing Claus converters and iseconomical to produce.

These and other objects which will become apparent to those skilled inthe art are accomplished by providing an activated alumina catalyst inwhich sodium oxide concentration, LOI and surface area of the catalystare controlled to achieve increased sulfur conversion. Sodium oxide maybe present in the catalyst in an amount greater than 0.50 wt % on an1100° C. calcined basis and is desirably about 1.0 to 2.5 wt %. Thechemical nature of the sodium compounds present in the catalyst isdifficult to specify under the conditions of use, so in practice, it ispreferable to relate the proportions of these compounds to that ofsodium oxide. The catalyst desirably has a specific surface area greaterthan 100 m² /g (BET) and an LOI (hydroxyl content determined by heatingfrom 400° to 1100° C.) of less than 6.0 wt %. The LOI may be less than5.0 wt % and is desirably about 2.0 to 4.0 wt %.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart which indicates the steps of the preferred methodfor making the catalyst of the present invention.

FIG. 2 is a graph in which percent sulfur conversion is plotted againstweight percent SO₂ chemisorbed on the catalyst of the present inventionat 316° C.

FIG. 3 is a comparative graph in which percent sulfur conversion isplotted against reactor temperature (°C.) at a constant gas spacevelocity of 1000 hr⁻¹. Sulfur conversion accomplished with activatedalumina having an LOI (hydroxyl content determined by heating from 400°to 1100° C.) of 2.2 wt % is compared with a catalyst having the sameproperties with the exception that its LOI (hydroxyl content determinedby heating from 400° to 1100° C.) value is 5.4 wt %.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The Claus catalyst of the present invention is an activated alumina inwhich sodium oxide is present in significant amounts, i.e. in amounts inexcess of 0.1 wt % of the catalyst. The sodium oxide content of thecatalyst is preferably greater than 0.50 wt %, with 1.0 to 2.5 wt % (onan 1100° C. calcined basis) being the most preferred range. The catalystof the present invention also has an LOI (hydroxyl content determined byheating from 400° to 1100° C.) less than the 6.0 wt % of typical priorart catalysts, with 2.0 to 4.0 wt % being the most preferred range.Another important feature of the catalyst of the present invention issurface area. High surface area, i.e. surface area greater than 100 m²/g (BET), is desirable with a surface area greater than 300 m² /g (BET)being particularly beneficial.

It has been found that each of these features, i.e. sodium oxidecontent, LOI and surface area, may be controlled singly or incombination in a manner such that sulfur dioxide chemisorption upon thecatalyst can be significantly reduced without requiring expensiverefining of the starting alumina. It has been determined that sulfurdioxide chemisorption under typical Claus reaction conditions proceedsin accordance with the equation:

    CS=0.00838 A+0.466 L-0.856 N-1.04±0.17                  (1)

where CS is chemisorption expressed as grams SO₂ per 100 grams Al₂ O₃ ;A is the catalyst surface area in m² /g; L is the percent hydroxylcontent determined by heating from 400° to 1100° C.; and N is thepercent sodium oxide on an 1100° C. calcined basis.

This equation expresses a surprising relationship between the variablesof surface area, LOI and sodium oxide. In order to achieve low SO₂chemisorption, the above equation indicates that a low LOI and/or highsodium oxide content are beneficial. For sodium oxide the opposite wasthought to be true. For example, low sodium oxide content was believedto be desirable by those skilled in the art because it was expected thatsodium oxide would react with sulfur dioxide to cause weight gain andchemisorption of SO₂ due to formation of sodium sulfite and/or sodiumsulfate. Such chemisorption would be expected to reduce availablesurface area of the catalyst and consequently decrease the sulfurconversion capability of the catalyst. Contrary to this expectation,significant amounts of sodium oxide are not only tolerable to a Clauscatalyst, but, in fact, are beneficial because, within certain limits,sodium oxide retards chemisorption of SO₂.

With respect to surface area, it is well established that the greaterthe surface area of a catalyst, the more active the catalyst. In view ofEquation (1), however, surface area is not as significant a feature aseither LOI or sodium oxide content. In fact, the proportion of theY-variance (wt % SO₂ chemisorbed) correlated by Equation (1) due tosurface area is only 22.9%, whereas, the proportion of the Y-varianceattributable to LOI and sodium oxide content is 39.2% and 34.2%,respectively.

That low chemisorption of SO₂ is desirable is shown in the graph of FIG.2. FIG. 2 relates percent sulfur conversion to wt % of SO₂ chemisorbedon the catalyst and shows that at 316° C. (a temperature which istypical in a Claus catalytic reactor), the reaction

    2H.sub.2 S+SO.sub.2 →2H.sub.2 O+3S

proceeds to almost 84% completion (i.e. formation of S) when thecatalyst has 2 wt % (on catalyst) SO₂ chemisorbed thereon. When the wt %SO₂ chemisorbed on the catalyst is 4 wt %, however, only 80% sulfurconversion is achieved. The Claus conversion efficiency (as indicated bypercent sulfur conversion) decreases linearly with increasing SO₂ weightgain on the catalyst over the range studied.

One method for making the catalyst of the present invention is outlinedby the flow chart in FIG. 1. It can be seen from the flow chart that asuitable starting material (such as Bayer trihydrate) is ground. Anaverage particle size of approximately 10 microns or less has been foundto be desirable. Appropriate grinding techniques are well known to thosein the art. After grinding, the particles are rapidly activated byexposure to relatively high temperatures for a brief period of time(i.e. less than one minute). The thus activated particles are then ballformed (i.e. agglomerated) in the presence of water and then aged for aperiod of time such as two hours. The aged material is then activated bysubjecting it to a temperature of 350° to 900° C. for a period of thirtyminutes to four hours, with the shorter times being used at highertemperatures. Temperatures of 400° to 500° C. for approximately two tofour hours would be typical activation conditions. The activatedmaterial is then ready for use in a Claus converter.

Starting materials suitable for the practice of the present inventioninclude pseudoboehmite, Bayer trihydrate or gibbsite, bayerite and anyother form of alumina which when properly treated yields an aluminacatalyst having a sodium oxide concentration of greater than 0.50 wt %(1100° C. calcined basis), an LOI (hydroxyl content determined byheating from 400° to 1100° C.) of 2.0 to 6.0 wt %, and a surface area of100 to 500 m² /g (BET). With respect to sodium oxide concentration as aconsideration in the choice of a starting material, it has been foundthat Bayer trihydrate, i.e. the product of the Bayer process, is aparticularly advantageous starting material because the relatively highNa₂ O concentration required in the catalyst of the present inventioncan be easily achieved. In the Bayer process, bauxite is treated withsodium hydroxide under pressure to form a sodium aluminate solution. Thesodium aluminate solution is decomposed and seeded with previouslyformed hydrate. The hydrate thus formed is then washed with water anddried. A typical Bayer hydrate contains 0.4 wt % of sodium oxide in itscrystal lattice, but this concentration may be lowered or raised by useof special temperature conditions and seed charges. Additionally, thesodium oxide content of Bayer alumina may be increased simply by washingthe precipitate from the sodium aluminate solution with less water. Thisdecreased washing represents a significant cost saving.

Where the starting material is pseudoboehmite made by rapidneutralization of NaAlO₂ by acids or acidic aluminum salts, the sodiumoxide concentration of the pseudoboehmite may be increased by using lesswash and repulp water (a dispersion medium) or by adding Na₂ SiO₃solution to the NaAlO₂ solution to form sodium zeolite prior toneutralization of the NaAlO₂ by addition of acid to the NaAlO₂ solution.Sodium zeolite powder or any other sodium source may also be added toactivated alumina by ball forming (agglomerating) the mixture to producean alumina having increased sodium oxide content. The addition of sodiumzeolite has the added advantage that the SiO₂ (silica) in the sodiumzeolite can contribute to thermal stability of the Claus catalyst totemperatures of about 500° C. Another method for increasing sodium oxidecontent of the alumina catalyst is to impregnate activated alumina withsodium hydroxide or some other sodium salt. For the latter method,however, it is necessary to take measures to assure that the pores ofthe catalyst are not blocked off. Other methods for increasing sodiumoxide content will be apparent to those skilled in the art.

The starting material of the present invention may have particles havinga particle size of 75 microns or larger. These particles should beground to a particle size of about 10 microns or less to achieve aparticularly advantageous Claus catalyst. Any grinding technique knownto those skilled in the art may be used.

Once the alumina starting material has an average particle size ofapproximately 10 microns or less, the alumina is rapidly activated byexposure to high temperature for a brief period of time. Methods forsuch rapid activation are well known in the art. One technique which hasbeen found to be particularly useful is that described in U.S. Pat. No.2,915,365. In accordance with this patented disclosure, aluminatrihydrate is injected into a stream of highly heated gases (e.g. air)at gas temperatures of greater than 300° C., such as 300° to 1000° C.,with 300° to 400° C. being the preferred range. The duration of contactbetween the alumina trihydrate and the hot gas may be less than oneminute, such as from a fraction of a second to several seconds, with twoto three seconds being the preferred contact time. The alumina, onceactivated, is in the gamma phase. If the hydrate were not ground priorto rapid activation, crystalline boehmite would be present in theactivated powder. The presence of boehmite is undesirable because itincreases the hydroxyl content (indicated by LOI) of the activatedalumina.

In a preferred embodiment of the present invention, the rapidlyactivated alumina is ball formed (agglomerated) in the presence of waterand then steam and water aged for a maximum of six hours at 60° to 80°C. and at pH's greater than 7. At high aging temperatures, greater than80° C., undesirable boehmite is formed in the alumina phase.

The above-described aging step is important to strength development andthe alumina phase chemistry of the agglomerates prior to activation.Aging is the recrystallization of activated (gamma) alumina back to thealuminum hydroxide phases of pseudoboehmite, boehmite, bayerite orgibbsite. Certain properties of the final activated product, includingcrushing strength and microstructural properties, are related to theextent of recrystallization or rehydration and also to the type anddegree of crystallinity.

For example, any of three types of aging may be used by those skilled inthe art: (1) natural, (2) steam and (3) water immersion. For naturalaging, the agglomerates are stored in moisture tight containers, and thewater in the agglomerate is permitted to rehydrate some of the gammaalumina. Addition of water to a closed hot container of agglomerates isknown as steam aging and allows for additional rehydration. In immersionaging the agglomerates are immersed into an aqueous medium. Immersionaging allows maximum rehydration of gamma alumina to the hydroxides.

The aged alumina may then be activated by any of a number of methodsknown to those skilled in the art. One method which yields a goodactivated alumina is to expose the aged alumina to a temperature in therange of 350° to 900° C. for a period of thirty minutes to about fourhours, with temperatures of 400° to 500° C. for two to four hours beingtypical conditions. Proper final activation, like powder activation andball aging of the agglomerates, is important in developing a Clauscatalyst with low LOI but high surface area. This activated alumina maythen be used in a standard Claus converter.

The activated alumina of the present invention may also be used as acatalyst base (support) to which small quantities of compounds known toenhance specific properties of the catalyst may be added. Such additivesinclude compounds of molybdenum, cobalt, nickel, iron, uranium, calcium,zinc, titanium, and others known to those skilled in the art.

Catalysts according to the invention can be used in a fixed or mobilebed or fluid bed or with aerial suspension, the dimensions of theconstituent grains being adapted to the particular situation.

Having thus described my invention, the following examples may behelpful in developing a better understanding thereof.

EXAMPLE 1

Activated alumina having the properties listed below was tested in abench Claus converter:

    ______________________________________                                        Al.sub.2 O.sub.3  (400 to 1100° C.)                                                         92.2 wt %                                                Na.sub.2 O (400 to 1100° C.)                                                                1.00 wt %                                                LOI (400 to 1100° C.)                                                                       6.58 wt %                                                Surface area         264 m.sup.2 /g (BET)                                     ______________________________________                                    

When starting up the bench scale Claus catalytic converter, it wasunexpectedly discovered that the activated alumina catalyst gainedweight while the reactor was above the sulfur dewpoint. The weight gainis attributable to SO₂ chemisorption on the catalyst.

In this particular experiment, the activated alumina catalyst was placedin the reactor and purged with oxygen-free, dry nitrogen at 316° C. for16 hours. This procedure stabilized the activated alumina surface areaand weight and removed all adsorbed H₂ O and O₂. The reactor was thenpurged with pure sulfur dioxide at a space velocity of 200 hr⁻¹, and theweight gain was measured as a function of time at 316° C. The resultswere as follows:

    ______________________________________                                        Cumulative    g SO.sub.2  % of Total                                          Minutes       100 g Catalyst                                                                            Wt. Gain                                            ______________________________________                                         0            0           0                                                   15            2.84        81.8                                                30            2.96        85.3                                                45            3.10        89.3                                                60            3.17        91.4                                                90            3.34        96.3                                                120           3.44        99.1                                                150           3.44        99.1                                                180           3.47        100.0                                               210           3.47        100.0                                               ______________________________________                                    

It can be seen that a major portion of the weight gain was achieved in arelatively short time, but three hours was chosen as the standardreference sorption time. A nitrogen purge at 316° C. for several hoursdid not decrease the weight gain, thus indicating the adsorption was notmerely physical adsorption but chemisorption.

The grams SO₂ chemisorbed at 316° C. per 100 grams of catalyst wascorrelated by the following equation:

    CS=0.00838 A+0.466 L-0.856 N-1.04

where, CS is chemisorption expressed as grams SO₂ per 100 grams Al₂ O₃ ;A is the catalyst surface area in m² /g (BET); L is wt % loss onignition from 400° to 1100° C.; and N is the wt % Na₂ O present (1100°C. basis). The predicted values corresponded to the measured valueswithin ±0.17.

Percent sulfur conversion was then calculated in accordance with theequation:

    % S conversion=87.5-1.86 (SO.sub.2)

where SO₂ is the wt % SO₂ chemisorbed on the catalyst. This calculatedvalue exactly corresponded with the measured value of 81.0% sulfurconversion.

EXAMPLES 2-9

Samples of activated alumina in which various surface area, LOI and wt %Na₂ O values were employed were tested in the same manner as Example 1.Chemisorption values were measured in each test after a standardreference time of three hours. The results are summarized in Table Ibelow.

                  TABLE I                                                         ______________________________________                                        g SO.sub.2          400-     1100° C.                                  100 g Al.sub.2 O.sub.3                                                                            1000° C.                                                                        Basis  Predicted                                 Ex-   Ac-    Pre-    S.A.,                                                                              LOI,   Na.sub.2 O,                                                                          % S                                   ample tual   dicted  m.sup.2 /g                                                                         wt %   wt %   Conversion*                           ______________________________________                                        2     4.49   4.29    390  5.24   0.44   79.1                                  3     3.16   3.29    357  5.37   1.36   81.6                                  4     3.76   3.94    332  5.50   0.43   80.5                                  5     3.73   3.76    381  4.21   0.41   80.6                                  6     2.58   2.73    244  3.87   0.09   82.7                                  7     2.53   2.49    363  4.91   2.10   82.8                                  8     2.62   2.46    243  3.32   0.10   82.6                                  9     2.47   2.48    315  2.49   0.33   82.9                                  ______________________________________                                         *using actual chemisorption values                                       

EXAMPLES 10-16

The relationship between Claus conversion (i.e. conversion to sulfur)and SO₂ chemisorption at 316° C. was studied more closely in theseexamples. The exact operating conditions are shown below. Varioussamples of activated alumina were used in a standard Claus converter,and the percent sulfur conversion was both measured and calculated bymeans of the equation discussed above. The results are summarized inTable II and graphically illustrated in FIG. 2.

                  TABLE II                                                        ______________________________________                                        Sample   Weight % SO.sub.2                                                                            % S Conversion                                        Number   on Catalyst    Actual   Predicted                                    ______________________________________                                        10       2.03           83.5     83.7                                         11       2.96           82.0     82.0                                         12       3.62           81.4     80.8                                         13       3.41           81.1     81.2                                         14       4.34           79.4     79.4                                         15       5.34           77.3     77.6                                         16       6.05           76.3     76.3                                         ______________________________________                                    

It can be seen from the data in Table II that the calculated percentsulfur conversion values correspond to those actually measured to ±0.3%.

    ______________________________________                                        Catalyst temperature                                                                              316° C.                                            H.sub.2 S/SO.sub.2 ratio                                                                          2.02                                                      GHSV* at 0° C. and 1 atm                                                                   4130 hr.sup.-1                                            N.sub.2              90.26 mole %                                             H.sub.2 S            6.51 mole %                                              SO.sub.2             3.23 mole %                                                                  100.00 mole %                                             Catalyst            Activated alumina                                                             4-8 mesh (3.57 mm)                                        Reaction 2H.sub.2 S + SO.sub.2 → 2H.sub.2 O + 3/X                      ______________________________________                                        S.sub.X                                                                        *GHSV = Gas Hourly Space Velocity                                        

EXAMPLES 17-18

These examples illustrate the effect of reactor temperature upon theconversion of COS to sulfur accomplished when an activated aluminacatalyst is used. The test conditions for each of these examples were asfollows:

    ______________________________________                                        Catalyst temperature                                                                              225-400° C.                                        GHSV at 0° C. and 1 atm                                                                    1000 hr.sup.-1                                            N.sub.2              92.35 mole %                                             COS                  1.08 mole %                                              SO.sub.2             6.57 mole %                                                                  100.00 mole %                                             Catalyst            Activated alumina                                                             12-14 mesh (1.30 mm)                                      Reaction 2 COS + SO.sub.2 → 2 CO.sub.2 + 3/X S.sub.x                   ______________________________________                                    

The alimina of Example 17 had a surface area of 315 m² /g (BET), an LOI(400° to 1100° C.) of 5.4 wt % and a Na₂ O content of 0.35 wt %. Thesulfur conversion achieved at the various temperatures tested isgraphically illustrated in FIG. 3 by the curve labeled 17.

The alumina of Example 18 had a surface area of 315 m² /g (BET), an LOI(400° to 1100° C.) of 2.2 wt % and a Na₂ O content of 0.35 wt %. Thepercent sulfur conversion achieved at the temperatures tested is showngraphically in FIG. 3 by the curve labeled 18.

FIG. 3 shows that the activated alumina having a lower LOI (400° to1100° C.) converts more COS to S at much lower temperatures than analumina having an LOI (400° to 1100° C.) value of nearly 6.0 wt % whichis typical of the alumina currently used in the art. In fact, it can beseen that the activated alumina of Example 18 converts COS to sulfuralmost 100% at approximately 300° C., whereas the activated alumina ofExample 17 requires a temperature of approximately 375° C. to achievecomparable results.

Having thus described my invention, I claim:
 1. An activated alumina catalyst containing sodium oxide, for promoting the reaction of hydrogen sulfide and sulfur dioxide so that such compounds may be removed from gases, the catalyst having increased resistance to sulfate poisoning and increased catalytic activity, characterized by the catalyst having a specific surface area greater than 100 m² /g (BET) and a sodium oxide content in an amount of 1.0 to 2.5 wt % (1100° C. calcined basis), the remainder being activated alumina.
 2. The catalyst of claim 1, wherein the LOI (400° to 1100° C.) is less than 6.0 wt %.
 3. The catalyst of claim 2, wherein the LOI is less than 5.0 wt %.
 4. The catalyst of claim 2, wherein the LOI is between 2.0 and 4.0 wt %.
 5. The catalyst of claim 2, wherein the surface area is greater than 300 m² /g (BET). 